CB400T Carb repair, etc

LongDistanceRider said:
Check that the 2 transition ports also pass fluid. It's hard to do with blocking off the main port, I use WD40 for that since it doesn't burn my eyes when it sprays sideways.
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I made 2 threaded inserts to only allow the red tube of the carb cleaner can to fit in to the idle adjust port, this way I didn't get spray all over me, and I seem to be getting fluid though to the centre port, if I block the small hole in to the carb throat. I also made a threaded insert to go in the the centre port for the same reason and I am getting fluid through to the idle adjust port. The press fit mettering jet is clear also, as are all of the other jets. Is this close to what you wanted me to check when you mentioned the 2 transition ports? Air is now passing well on both carbs. 19.jpg
 
LongDistanceRider said:
The aluminum plug is the floor of the idle circuit passage under the 2 transition ports.
Do not use anything hard to poke into the transition ports.
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Reviewing this thread's post #33 (the one with the cut-away carb body illustrated with red and blue lines)
it appears that the 2 transition ports are the ones between the aluminum plug and the throat of the carb.
And, I think he meant to type that it's hard to check that WD-40 fluid passes thru them WITHOUT blocking off the main port
 
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Boosted said:
Reviewing this thread's post #33 (the one with the cut-away carb body illustrated with red and blue lines)
it appears that the 2 transition ports are the ones between the aluminum plug and the throat of the carb.
And, I think he meant to type that it's hard to check that WD-40 fluid passes thru them WITHOUT blocking off the main port
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Yes, that's what I mean. You can actually screw the mixture screw all the way in to block the main port, by doing so if you also block the 2 transition ports with a finger you can check that the mixture screw is actually closing off the port.
 
The VB's are a difficult carb set to clean correctly as all these posts have noted. You are well on your way though now it seems and when working correctly they are a great carb set to have on the bike.

Very clean looking bike too and it will be a great ride once these carbs are sorted out.

As a future note when storing the bike make sure you totally drain the carbs of all gas through the drain screws for the winter layup. Disconnect the fuel line to the carbs too, if you leave the gas tank full and on the bike for storage. Leaving any modern gas in them over the winter will have you back to square one again.
 
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It is a super nice clean looking bike! And I have to admit being wrong if those idle jets came out looking clean as you show. Maybe I do need an ultrasonic cleaner. I would suggest to research and give some careful attention to the rough sync of the two throttle plates and the nominal suggested crack open. I've never done or had the proper vacuum guages or funky screw driver to do the sync job properly. I did blow threw them with my mouth to get a feel if they were the same. That's a little strange and probably not recommended, just came up with the idea myself. ;) I recall using some suggested wire guage to measure it.
 
kbongos said:
It is a super nice clean looking bike! And I have to admit being wrong if those idle jets came out looking clean as you show. Maybe I do need an ultrasonic cleaner. I would suggest to research and give some careful attention to the rough sync of the two throttle plates and the nominal suggested crack open. I've never done or had the proper vacuum guages or funky screw driver to do the sync job properly. I did blow threw them with my mouth to get a feel if they were the same. That's a little strange and probably not recommended, just came up with the idea myself. ;) I recall using some suggested wire guage to measure it.
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Well, I will attach a pic of what the bike looked like when I started. It was covered in overspray and it took about three hours to wet sand and polish the tank, side covers, fender and all of the bright work. This task will continue in the spring. The master cylinder was full of sludge, and that was an experience to rebuild. The rear wing behind the seat had to be repaired, it was split. Also, I did purchase a set of vacuum gauges with head adapters to synchronize the carbs properly, and this will happen when I get them back on the bike. Over all I am finding this bike to be a lot of fun to work on, and so far, above 4500 RPM, quite responsive! Hopefully the carbs work this time, if not, off they come again. Thanks for your insight!20.jpg
 
Bob, you'll find that all these smaller twins run best when the full rpm range is used, they were designed to turn high revs and they hit their sweet spot around the time many feel it's time to shift because they're not used to hearing engines turning higher rpm levels.
 
ancientdad said:
Bob, you'll find that all these smaller twins run best when the full rpm range is used, they were designed to turn high revs and they hit their sweet spot around the time many feel it's time to shift because they're not used to hearing engines turning higher rpm levels.
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Well, after having a 1200 Sportster and a 96ci Super glide, this is a different bike for sure. The short ride that I did have on it was a lot of fun. I am really looking forward to having it run well again. At my age, smaller and lighter just seems like a good idea! Also, I am going to try to add (2) inline filters to the fuel line from the gas tank, just in case. I purchased a new petcock, one with a good fine mesh stainless screen inside the tank just to try to make sure that no dirt gets in to these carbs. The petcock also has a removable sediment bowl which will help keep an eye on things. When I poured out the tank, then added gas, shook it, then poured it out again there wasn't any rust or dirt, but having filters is a good idea, I feel. Red line is 10, and I have a feeling we will become good friends! Thanks!
 
LongDistanceRider said:
Shift in the 6-7K range, keep the rpm above 4K while cruising. Don't be afraid of the redline but really you'll find that @9K the power flattens.
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Sounds like sound advice to me. It will probably take a bit to get used to a 6-7 shift range, after what I've grown used to. The first short ride has shown me that this is a very smooth engine, very well put together. Thanks!
 
I have the carbs back on the bike again. I will take some time to figure out a good fuel line delivery with filters in it before I try to start it again. Those boots that connect the carbs to the air box are a real challenge to get on!
 
Bobs twin said:
I have the carbs back on the bike again. I will take some time to figure out a good fuel line delivery with filters in it before I try to start it again. Those boots that connect the carbs to the air box are a real challenge to get on!
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I hear ya, cold and stiff doesn't go with easy squeezy.
 
Yes, I recall having trouble first few times I took carbs out with those back boots to air box. A long time ago I loosened up the back air box enough so I can just take the front boots out. A little awkward to get the 2 inner bolts on these boots out, but not too bad. Then just loosen up the clamps on back boots at carbs and pull back to get room to pull front boots out of place. Then just disconnect the choke and throttle lines and they are out. i forget exactly what I did to loosen up that air box, it was a long time ago. I think I have a missing or loose bolt somewhere to leave them loose. I will be re-investigating this when I eventually pull carbs from my more recently acquired CM450 bike. Maybe I don't need to loosen airbox, which was some work finding the bolts for this in difficult spots.
 
well..................
I don't want you to laugh too hard, but............
I have the bike running again, and I now have low speed, or idle adjustment, which is good.
but...............
I took it for a ride, and I no longer have high speed, or the carbs are not opening up.
I put it away for the day.................
I can only handle so much.
Bob
 
Nobody's laughing Bob, we've all been there at some point. Hard to say what is wrong based on what you've said, but since this is Jim' wheelhouse he might have an idea of what may have happened.
 
It's pretty chilly there today but not cold enough to have iced the carbs in most cases.
Was the airbox connected? If not then that's the probable cause, these carbs really like the airbox.
 
LongDistanceRider said:
It's pretty chilly there today but not cold enough to have iced the carbs in most cases.
Was the airbox connected? If not then that's the probable cause, these carbs really like the airbox.
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Yes, it is cold, that's for certain.
The airbox is connected, boots, air filter and all.
I will let it sit for now. I may have another look another day.
I might try to take the hats off of the top of the carbs to make sure there is nothing stopping them from lifting.
I was pleased to have low speed this time, it now should transition between low speed and high speed, when I find out what is wrong.
It was me that laughed when I brought the bike back in to the garage. I had to giggle, I've spent a lot of time getting the low speed circuits to work, and I just assumed that the high speed side would work, like it did the last time. Oh well, maybe it will be better another day. Bottom line, I am not giving up on this bike!
 
I put some brass seats in backwards and it ran horrible, fortunately was able to fix that. Good news is you will be able to work on those carb in a fraction of the time now that you have done it.
 
Has anyone tried to remove the carb set by taking the bolts out of the short intake manifolds on the heads and removing them as an assembly? I was wondering if this might be any easier?
 
Bobs twin said:
Has anyone tried to remove the carb set by taking the bolts out of the short intake manifolds on the heads and removing them as an assembly? I was wondering if this might be any easier?
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Yes, that is how I removed the carbs rack on mine. And when I reinstalled the rack assembly, I put new rubber o-rings into the groove of each "insulator" (intake manifold) that seals them to the engine's cylinder head so there won't be an air-vacuum leak.
Correct o-ring size is 40mm X 2.4mm but a local hydraulics service business which stocks a large assorted variety of o-rings had some that fit the grooves (41x2.5mm, 70 durometer-hardness) so I bought them there ($0.70 each) instead of paying a lot more and waiting for my local Honda motorcycle dealer to order the genuine Honda ones in.
And, just like the grooves on the float bowls, the grooves of the insulators have "pinchers?" that hold the rubber o-ring gasket in place so to help with re-installation of the rack assembly to the engine.
They're number 11 on this:
 
Boosted said:
Yes, that is how I removed the carbs rack on mine. And when I reinstalled the rack assembly, I put new rubber o-rings into the groove of each "insulator" (intake manifold) that seals them to the engine's cylinder head so there won't be an air-vacuum leak.
Correct o-ring size is 40mm X 2.4mm but a local hydraulics service business which stocks a large assorted variety of o-rings had some that fit the grooves (41x2.5mm, 70 durometer-hardness) so I bought them there ($0.70 each) instead of paying a lot more and waiting for my local Honda motorcycle dealer to order the genuine Honda ones in.
And, just like the grooves on the float bowls, the grooves of the insulators have "pinchers?" that hold the rubber o-ring gasket in place so to help with re-installation of the rack assembly to the engine.
They're number 11 on this:
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Good to know, and thanks!
I'll try this the next time I remove the carbs.
 
Bobs twin said:
Good to know, and thanks!
I'll try this the next time I remove the carbs.
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Boosted said:
Yes, that is how I removed the carbs rack on mine. And when I reinstalled the rack assembly, I put new rubber o-rings into the groove of each "insulator" (intake manifold) that seals them to the engine's cylinder head so there won't be an air-vacuum leak.
Correct o-ring size is 40mm X 2.4mm but a local hydraulics service business which stocks a large assorted variety of o-rings had some that fit the grooves (41x2.5mm, 70 durometer-hardness) so I bought them there ($0.70 each) instead of paying a lot more and waiting for my local Honda motorcycle dealer to order the genuine Honda ones in.
And, just like the grooves on the float bowls, the grooves of the insulators have "pinchers?" that hold the rubber o-ring gasket in place so to help with re-installation of the rack assembly to the engine.
They're number 11 on this:
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Thank you for the info on the O-rings required. We have a parts supply here in Ontario, Canada that has been very good for what I need. I ordered (8) of these gaskets, they worked out to about $1.25 CDN, which is about $0.37 in real money, or in American funds. Yes, I think Monopoly money is worth more than our tender! At any rate, I am considering removing the carbs one more time to check the passages that must provide the vacuum for the carb slides, just have to figure out where to look. I am trying to look at this positively; they did work before the second and third ultrasonic cleaning. Thanks again!
 
Remember, you can access the (piston) slides with the rack installed by simply removing the seat and gas tank and removing the carbs' top covers, big springs, and piston-slides and then the kidneybean-shaped black plastic piece in each one. Then you could air blow passages there without having to remove the rack.
 
Boosted said:
Remember, you can access the (piston) slides with the rack installed by simply removing the seat and gas tank and removing the carbs' top covers, big springs, and piston-slides and then the kidneybean-shaped black plastic piece in each one. Then you could air blow passages there without having to remove the rack.
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Yes, I am doing this at the present time. I am just trying to make sure that I give these carbs the best chance that I can, to work properly again. But thanks for your guidance, I will have a look under the covers again, remove the black plastic cover and blow the passages clear. Will this affect any other part of the carb? Should I drain the bowls before I start? For me, because I have had high speed function from these carbs before, it should be able to be restored again, hopefully.
 
A question. Should I consider replacing the air cut-off diaphragms, and possibly the accelerator pump? When I had the carbs apart all seemed fine, no cracks or problems were present.
Bob
 
What were the results of the Ignition Diagnosis checks?
Are all 3 idle/transition ports flowing fluid?
Does the accel pump actually spray out the nozzles by the choke plate?
Instead of using terms like high and low speed it's much better to reference rpm's since the other terms are subject to interpretation. High speed to me means 7,500 plus, low speed means idle to 4,000.
Personally I block off the air cut valve vacuum port leaving the valve in place. All it does is mitigate some decel afterburn/popping while also giving the potential for an undiagnosable vacuum leak.
 
Bobs twin said:
I have the bike running again, and I now have low speed, or idle adjustment, which is good.
but...............
I took it for a ride, and I no longer have high speed, or the carbs are not opening up.
Click to expand...
Click to expand...
As Boosted suggested, focus on those large jet's as obviously they are for high speed/power. I recall them having a few tricky components that had to be lined up and in the right direction. Take the hats off and compare carefully. With carbs off I recall you can push the needles up and get a feel for travel and seating. Focus on any changes you made as it worked for high speed previously, eh? That last eh I threw in because you are in Canada ;) Hope to take mine out for a ride tomorrow, temperatures to get up to 50F.
 
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Bobs twin said:
Should I consider replacing the air cut-off diaphragms, and possibly the accelerator pump? When I had the carbs apart all seemed fine, no cracks or problems were present.
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If the cut-off and accelerator pump diaphragms are still sufficiently flexible and without tears, or splits, or cracks in their rubber they should be re-usable. But, if you think that the rubber has become too stiff from age and use (heat-cycles), then replacing them might help your current problem, use your best judgement.

If you decide to replace, shop prices at both Sirius Consolidated Inc. in Ontario (or Toronto?) www.siriusconinc.com, or their eBay store, and the various sellers on eBay.
PRICES DIFFER SIGNIFICANTLY.
Sirius carries Japanese ones by "Keyster". The other Japan-made ones are by either K&S or K&L.
If when on eBay it isn't K&L or K&S, then it's Chinese. I bought Chinese whole-carb-kits from eBay before I learned about Sirius, Keyster, K&S, and K&L.
 
When doing an in-depth carb cleaning and rebuild I always replace the accelerator pump diaphragm regardless. The air cuts less so if they look good they can be reused and are readily available.
The accelerator pump circuit you want at 100% and a used diaphragm, even one that looks OK may not be at its best.

Just my personal opinion and practice.
 
Boosted said:
If the cut-off and accelerator pump diaphragms are still sufficiently flexible and without tears, or splits, or cracks in their rubber they should be re-usable. But, if you think that the rubber has become too stiff from age and use (heat-cycles), then replacing them might help your current problem, use your best judgement.

If you decide to replace, shop prices at both Sirius Consolidated Inc. in Ontario (or Toronto?) www.siriusconinc.com, or their eBay store, and the various sellers on eBay.
PRICES DIFFER SIGNIFICANTLY.
Sirius carries Japanese ones by "Keyster". The other Japan-made ones are by either K&S or K&L.
If when on eBay it isn't K&L or K&S, then it's Chinese. I bought Chinese whole-carb-kits from eBay before I learned about Sirius, Keyster, K&S, and K&L.
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I just checked out Sirius, and this is a good source, thanks!
Bob
 
kbongos said:
As Boosted suggested, focus on those large jet's as obviously they are for high speed/power. I recall them having a few tricky components that had to be lined up and in the right direction. Take the hats off and compare carefully. With carbs off I recall you can push the needles up and get a feel for travel and seating. Focus on any changes you made as it worked for high speed previously, eh? That last eh I threw in because you are in Canada ;) Hope to take mine out for a ride tomorrow, temperatures to get up to 50F.
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Yup, I noticed the "eh", nice touch and thanks. I actually took some courses years ago in Cincinnati, and they didn't believe that I was from Canada, because I didn't say "eh". Fond memories!
 
LongDistanceRider said:
What were the results of the Ignition Diagnosis checks?
Are all 3 idle/transition ports flowing fluid?
Does the accel pump actually spray out the nozzles by the choke plate?
Instead of using terms like high and low speed it's much better to reference rpm's since the other terms are subject to interpretation. High speed to me means 7,500 plus, low speed means idle to 4,000.
Personally I block off the air cut valve vacuum port leaving the valve in place. All it does is mitigate some decel afterburn/popping while also giving the potential for an undiagnosable vacuum leak.
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Jim, I haven't done the diagnostics as yet, it's kinda cold out there. (I am no electrician, but feel that cold can affect results.) I did get fluid to flow well after removing the press in jet though. The way that the bike felt when I rode it was that there was no transition between low speed and high speed, or the pistons were not lifting allowing fuel to come from the main jet. I am close to pulling the carbs again to have another look, my arthritis doesn't enjoy below zero as much anymore. And yes, the bike now seems to run fairly well up to 4000, but will not go above that. When I first took it out it was great above 4000, but nothing below. The accel pump does spray fluid out of the nozzles also, so I feel that for now it is working.
Bob
 
Ah, Arther is one of your friends:cry: I'm getting to know him occasionally.
I would do the ignition diagnosis next before investing any more time/effort into the carbs.
 
LongDistanceRider said:
Ah, Arther is one of your friends:cry: I'm getting to know him occasionally.
I would do the ignition diagnosis next before investing any more time/effort into the carbs.
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I appreciate your sound advice. I'll have a look at the checks that you recommend as soon as the seasons festivities subsist.
In the mean time, have a very Merry Christmas, and a Happy New Year!
 
well guys........
someone just got back from a decent ride!
yup!
she's alive!
now............
I haven't done any setup on the carbs as to vacuum and idle mixture settings, but the carbs work.
they actually work!
I took them off one more time and did a complete rebuild, including new air cut-off and accelerator pump diapragms.
I ordered the kits from Sirius, and a member recommended them, they sell quality stuff for sure, thanks!
I have to figure out a routing to incorporate an inline filter, which will allow the side cover to go back on, but that's minor.
Took it up to 100, no problem!
my hands are frozen.......... there's a l;ittle snow on the ground, but hey.................
it runs!
Bob
 
Glad to hear it's running. With inline filter you have a few options...

K&N makes one that looks like it will work OK: https://www.amazon.com/K-N-81-0221-Fuel-Filter/dp/B000E2AR70/
There are Briggs and Stratton clones that work fine, I've used them for years: https://www.amazon.com/Carbbia-Stratton-AM107314-LG298090-LG298090S/dp/B0B2WRYPFL

Whatever you use, be sure to use the 5.5mm fuel line from the dealer (or order it) and use the clips. Don't use 1/4" lawn mower hose or the 1/4" worm gears. What happens is that it will leak at the barb on the carbs and make you think the bowl is leaking. It also tends to chunk off after a couple of years. OK in an emergency, but don't rely on it.
 
Maraakate said:
Glad to hear it's running. With inline filter you have a few options...

K&N makes one that looks like it will work OK: https://www.amazon.com/K-N-81-0221-Fuel-Filter/dp/B000E2AR70/
There are Briggs and Stratton clones that work fine, I've used them for years: https://www.amazon.com/Carbbia-Stratton-AM107314-LG298090-LG298090S/dp/B0B2WRYPFL

Whatever you use, be sure to use the 5.5mm fuel line from the dealer (or order it) and use the clips. Don't use 1/4" lawn mower hose or the 1/4" worm gears. What happens is that it will leak at the barb on the carbs and make you think the bowl is leaking. It also tends to chunk off after a couple of years. OK in an emergency, but don't rely on it.
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I ordered two different filters from amazon, and I am currently using the 90deg one. My problem is trying to find the room to put one on the bike and still be able to put the side cover on. There isn't a lot of space. I will attach pics of the 2 filters I received.
bob
filter1.jpgfilter2.jpg
 
I've never used an extra fuel filter on any of my bikes. Even the road bike that's toured the US twice has never had one. The screen mesh petcock filter in the tank will handle all those needs.
 
LongDistanceRider said:
I've never used an extra fuel filter on any of my bikes. Even the road bike that's toured the US twice has never had one. The screen mesh petcock filter in the tank will handle all those needs.
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well, my concern is that the tank sat for 37 years, and I didn't do the vinegar treatment to clear the surface rust. I felt that putting vinegar in the tank with screws, due to the close areas inside, and the petcock and filler spouts extending in to the tank, I'd never get the screws or all of the vinegar back out. So I am trying to add some extra protection. When I flushed the tank with gas the gas was clean when I took it out.
I did purchase and install a new petcock with a good fine mesh screen in it.
So this is where I am.
Bob
 
Bobs twin said:
well, my concern is that the tank sat for 37 years, and I didn't do the vinegar treatment to clear the surface rust. I felt that putting vinegar in the tank with screws, due to the close areas inside, and the petcock and filler spouts extending in to the tank, I'd never get the screws or all of the vinegar back out. So I am trying to add some extra protection. When I flushed the tank with gas the gas was clean when I took it out.
I did purchase and install a new petcock with a good fine mesh screen in it.
So this is where I am.
Bob
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I've never bothered to fully clean out a tank with vinegar unless its so far rusted. If its some surface rust on the inside of the tank the petcock filter is more than sufficient. An inline filter will fit on these bikes just fine if you're worried. The red ones I linked to work fine and fit well.
 
Maraakate said:
I've never bothered to fully clean out a tank with vinegar unless its so far rusted. If its some surface rust on the inside of the tank the petcock filter is more than sufficient. An inline filter will fit on these bikes just fine if you're worried. The red ones I linked to work fine and fit well.
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OK, I'll order some of those then.
Thanks!
bob
 
I now have an inline filter in place that works and doesn't leak, should be fine for vibration, and not rubbing on things.
the idle mixture is adjusted also, (a few times).
and I also set the vacuum between the 2 carbs to synchronize them.
it is running pretty good now.
next............
set and check the valves.
bob
 
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